A Power Control MAC
Protocol for Ad Hoc
Networks
EUN-SUN JUNG, NITIN H. VAIDYA,
Wireless Networks 11, 55–66, 2005.
Speaker: Han-Tien Chang
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Outline



Introduction
Related Work
IEEE 802.11 MAC Protocol



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BASIC Power Control Protocol
Proposed Power Control MAC Protocol
Performance Evaluation
Conclusions
Comments
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Introduction

Wireless hosts are usually powered by
batteries which provide a limited amount of
energy.

Power saving


Enter a doze state by powering off its wireless network
interface
Power control


suitably vary transmit power to reduce energy
consumption
used to improve spatial reuse of the wireless channel
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Introduction (cont’d)

A simple power control protocol has been proposed
based on an RTS–CTS based IEEE 802.11 network
[1,6,10,15].




RTS and CTS are transmitted using the highest power
level
DATA and ACK are transmitted using the minimum power
level necessary for the nodes to communicate
Increases collisions and degrades network throughput
In this paper, they present a new power control
protocol which does not degrade throughput.
[1] S. Agarwal, S. Krishnamurthy, R.H. Katz and S.K. Dao, Distributed power control in ad-hoc wireless networks, in: Proc. PIMRC01 (2001).
[6] J. Gomez, A.T. Campbell, M. Naghshineh and C. Bisdikian, Conserving transmission power in wireless ad hoc networks, in: Proc. ICNP’01 (November 2001).
[10] P. Karn, MACA – a new channel access method for packet radio, in: Proc. 9th ARRL Computer Networking Conference (1990).
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[15] M.B. Pursley, H.B. Russell and J.S.Wysocarski, Energy-efficient transmission and routing protocols for wireless multiple-hop networks and spread-spectrum
radios, in: Proc. EUROCOMM 2000 (2000) pp. 1–5.
Related Work

Power control mechanism

be incorporated into the IEEE 802.11 RTS–CTS
handshake is proposed in [10,15].



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Node A, to specify its current transmit power level in
the transmitted RTS
Allows receiver node B to include a desired transmit
power level in the CTS sent back to A.
On receiving the CTS, node A then transmits DATA
using the power level specified in the CTS.
Maintain a desired signal-to-noise ratio of node B.
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Related Work (cont’d)



Transmit power is controlled according to packet size
in [4,5].
IEEE 802.11 may result in unfairness for nodes which
use lower transmission power than their neighbor
nodes. [14] propose a scheme to improve the fairness.
Power Controlled Multiple Access (PCMA) protocol
[12]

PCMA uses two channels, one channel for “busy tones”,
and the other for all other packets.
[4] J.-P. Ebert, B. Stremmel, E. Wiederhold and A. Wolisz, An energyefficient power control approach for WLANs,
Journal of Communications and Networks 2(3) (2000) 197–206.
[5] J.-P. Ebert and A. Wolisz, Combined tuning of RF power and medium access control for WLANs,
in: Proc. IEEE International Workshop on Mobile Multimedia Communications (MoMuC’99) (November 1999).
[12] J.P. Monks, V. Bharghavan and W.M.W. Hwu, A power controlled multiple access protocol for wireless packet networks,
in: Proc. INFOCOM 2001 (April 2001).
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[14] N. Poojary, S.V. Krishnamurthy and S. Dao, Medium access control in a network of ad hoc mobile nodes with heterogeneous
power capabilities, in: Proc. IEEE International Conference on Communications (ICC 2001), Vol. 3 (2001) pp. 872–877.
IEEE 802.11 MAC Protocol

Distributed Coordination Function



Transmission Range
Carrier sensing range
Carrier sensing zone
250m
550m
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IEEE 802.11 MAC Protocol (cont’d)
The EIFS interval begins following indication by the physical layer that the
channel is idle after sensing of the erroneous frame.
The purpose of EIFS is to protect an ACK frame at the source node.
EIFS = SIFS+ DIFS+ [(8 * ACK-size)+PreambleLength+ PLCPHeaderLength] / BitRate
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IEEE 802.11 MAC Protocol (cont’d)

Hidden terminal problem


nodes in the receiver’s carrier sensing zone, but
not in the sender’s carrier sensing zone or
transmission range
can cause a collision with the reception of a DATA
packet at the receiver
A
B
C
D
E
F
Hidden node
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BASIC Power Control Protocol

One simple solution



As a modification to IEEE 802.11
Transmit RTS and CTS at the highest possible power
level
Transmit DATA and ACK at the minimum power level
necessary to communicate
1. A destination node receives an
RTS, it responds by sending a CTS
as usual (at power level pmax).
2. When the source node receives the
CTS, it calculates pdesired
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BASIC Power Control Protocol (cont’d)

Deficiency of the BASIC protocol

The power control mechanism causes



The transmission range and carrier sensing range
become smaller.
The data transmission cannot be detected by some
nodes which may interfere the current transmission.
More prone to collisions, degrading throughput (as
shown in the later simulations)
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BASIC Power Control Protocol (cont’d)
1.
2.
3.
4.
D sends RTS.
E sends CTS.
Data from D to E
ACK from E to D
5. H can hear CTS, but
cannot hear data tx.
6. H will interfere the
current transmission
when H starts
transmitting
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Proposed Power Control MAC (PCM)
Protocol

The procedure used in PCM




Source and destination nodes transmit the RTS and CTS
using pmax
Nodes in the carrier sensing zone set their NAVs for EIFS
duration when they sense the signal and cannot decode it
correctly
The source node may transmit DATA using a lower power
level, similar to the BASIC scheme.
To avoid a potential collision with the ACK (as discussed
earlier)
 The source node transmits DATA at the power level pmax,
periodically.
 For just enough time so that nodes in the carrier sensing
zone can sense it.
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Proposed Power Control MAC Protocol (cont’d)

The key difference between PCM and the BASIC
scheme



The PCM periodically increases the transmit power to
pmax during the DATA packet transmission.
15μs should be adequate for carrier sensing in [22]
EIFS duration is set to 212μs using a 2 Mbps bit rate


In PCM, a node transmits DATA at pmax every 190μs for a
20μs duration.
Thus, the interval between the transmissions at pmax is
210μs, which is shorter than EIFS duration.
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[22] The Editors of IEEE 802.11, Wireless LAN Medium Access Control (MAC) and Physical Layer (PHY) Specification (1997).
Proposed Power Control MAC Protocol (cont’d)
The procedure graph of PCM
The interval between the transmissions at pmax
The time of carrier sensing and
increasing/decreasing output power
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Performance Evaluation

Simulated schemes

BASIC, PCM, PCM40 and IEEE 802.11


PCM40increase the transmit power every 170μs for
40μs during DATA transmission
Two metrics


aggregate throughput over all flows in the network
total data delivered per unit of transmit energy
consumption (Mbits delivered per Joule)
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Performance Evaluation (cont’d)

Simulation model and topology


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Use ns-2 with CMU wireless extension
All simulation results are the average of 30 runs.
Each simulation runs for 20 seconds of simulation time.
Topology
 Chain Topology



vary the distance from 40 m to 250 m
Random topology: one hop flows
Random topology: multi-hop flows
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Performance Evaluation (cont’d)

Chain Topology: varying node distance
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Performance Evaluation (cont’d)
Chain Topology: varying network load (one hop flow)
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Performance Evaluation (cont’d)
Random topology: network load / different 50 scenarios
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Performance Evaluation (cont’d)
Random topology
multi-hop flow
Random topology: varying packet size
(one hop flow)
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Conclusions
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

Overcome the shortcoming of the BASIC power
control protocol
PCM achieves energy savings without causing
throughput degradation
One possible concern with PCM


It requires a frequent increase and decrease in the transmit
power which may make the implementation difficult.
Future work includes the development of a power
control MAC protocol that conserves energy while
increasing spatial reuse.
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Comments



Find the deficiency of other works
Improve the power control mechanism by a
simple manner
Various simulation scenarios to support the
proposed mechanism
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